Heat pump defrost control unit



Oct. 25, 1966 o. F. KAYL 3,280,579

HEAT PUMP DEFROST CONTROL UNIT CONTROL umT I ELEMENT 1 E ELEMENT 2ELEMENT 3 i 1/ OUTSIDE COlL 4-WAY REVERSING COMPRESSOR VALVE mswE COIL

REVERSING VALVE CONTROL INVENTOR W' 1 DARYL F. KAYL ATTORNEY Oct. 25,1966 D. F. KAYL HEAT PUMP DEFROST CONTROL UNIT 2 Sheets$heet 2 FiledSept. 10, 1964 INVENTOR DARYL F. KAYL ATTORNEY United States Patent3,286,579 HEAT FUMP DEFRGST CONTROL UNIT Daryl F. Ka-yi, 2751 6th Ave.,Merced, Calif. 95340 Fiied Sept. 10, 1964, Ser. No. 395,452 1 Claim.(Cl. 62--156) This invention relates to coil frost control for anair-toair heat pump apparatus and more specifically to a defrost systemutilizing two separate cycle controls.

It is well known that in heat pumps of the air-to-air type, heat isextracted from one source of air and rejected to another. When a heatpump is employed to supply heated air to a space, heat extracted from asource of air flowing over an outdoor heat transfer coil is rejected toa stream of air flowing over a heat transfer coil located in an insidespace being treated. Under circumstances where the ambient temperatureis substantially reduced, the amount of heat in the outdoor air islikewise relatively reduced.

Basically, in a heat pump, a charge of refrigerant is sealed in a closedcircuit. This refrigerant is changeable between its liquid and vaporstates at the normal heat pump temperatures and at the commerciallyoperable pressures. A compressor is utilized to compress the vaporousrefrigerant after which the refrigerant is directed to a condenser coil.The heat transfer between the condenser coil and the ambient fluidwithdraws heat from the refrigerant thereby condensing the refrigerantto a liquid at high pressure. This liquid refrigerant is then throttledinto an evaporator coil so that the pressure of the liquid refrigerantis less than the vapor pressure of the refrigerant ambient in theevaporator coil. Due to the heat transfer between the evaporator coiland the fluid adjacent thereto, the low pressure liquid refrigerant iscaused to boil and become a vapor. This vapor is then returned byappropriate conduits to the compressor for recycling.

It is well known that the surface of the evaporator coils tends toaccumulate frost thereon. This is due to the fact that when the surfacetemperature of the coil drops below 32 degrees Fahrenheit, any moisturecondensed out of the air flowing over the coil will freeze on thesurface of the evaporator coil. Any build up of frost or ice on theevaporator coil acts as an insulator, decreasing the rate of heattransfer through the coil and substantially minimizing the efficiency ofthe refrigeration cycle and may eventually render it ineffective. It istherefore apparent that it is not only desirable, but mandatory, toprovide some means for preventing excessive frost accumulation.

The defrosting of an evaporator coil may be accomplished in a variety ofways which are Well known. Included in these methods are the stopping ofthe refrigeration cycle, followed by either blowing warm air over theevaporator coil, or discharging the relatively warm condenser gas intothe evaporator coil. It is apparent that this is neither an eflicientnor desirable method of solving the problem of frost accumulation.

Simple thermostats or pressure switches have also been used. Thesedevices either cut out or initiate the defrost cycle when a drop in thepredetermined evaporator suction temperature is detected and cut back inwhen the defrost cycle is completed as the result of reaching a suctiontemperature in excess of 32 degrees. Another defrosting method includesa device which responds to the static pressure drop in the air streampassing over the coils. Another responds to the velocity of the airpassing through the coil. The latter two types are difficult to keep inadjustment since they are constantly exposed to cold temperatures andthe temperature or pressure responsive devices are not adequate becauseof the wide range of evaporator coil temperatures normally encounteredeven in the absence of frosting.

Temperature sensing bulbs have previously been disposed in spacedlocations, but systems of this type often result in false and/or earlydefrost cycle termination, to the end that either a short cycling of theequipment or an excessive accumulation of frost results. Moreover,apparatus of this type has been hampered by the lack of adjustable,separate initiation and termination controls.

It is therefore an object of this invention to provide a separate, fullyadjustable initiation and termination control.

It is a further object of this invention to provide control means whichwill terminate defrost only when the outlet line temperature indicates acondition reflecting a complete defrost of outside coil.

It is a still further object of this invention to provide two separatecycle controls in one case.

An additional object of this invention is to provide a device whichprecludes false and/ or early termination of the defrost cycle.

The foregoing objects and advantages are provided by this inventionwhich utilizes three power elements connected to temperature sensingdevices which operate one set of contacts in an electrical switchingmeans. Specifically, two of the three power elements are on a hingedlever operatively connected so that only the differential between thetwo is active. When this differential, brought about by the frosting ofthe coil, is great enough, as measured across the coil-heat exchanger,the resultant force opens one pair of contacts and closes a second set.This action accomplishes two things, first, air flow across the blockedcoils is stopped and second, the position of a four-way reversing valvewhich circulates hot gas through the coil to be defrosted is reversed.

The third power element is then actuated which in turn actuates anauxiliary heating system which may continue the flow of warm air throughheating ducts if the system is being used in that mode. This third powerelement also operates to reverse the process by resetting the originalcontacts when defrost is completed, for example, when the temperature ofthe outside coil has reached a preset value. in the inventive device,both differential and termination elements are adjustable.

Other objects and advantages of the invention will be apparent from thefollowing detailed description of the invention when taken in referenceto the accompanying drawings wherein:

FIGURE 1 is a block diagram of an air-to-air heat pump system utilizingthe invention;

FIGURE 2 is a more detailed schematic view of FIG- URE 1.

As shown in FIGURE 1, the system basically comprises a pair of coiledheat exchangers interconnected by piping, a four-way reversing valve anda compressor. The operation of the system is controlled by a controlreversing valve 17 the refrigerant flows to the unit which initiates thereversing valve control. Three capillary reference elements are disposedso that the control unit contains two separate cycle controls in asingle case.

FIGURE 2 depicts a more detailed schematic view of the invention inwhich an inside heat exchanger or coil 11 is interconnected with anoutside heat exchanger or coil 13 by a compressor 15, a four-wayreversing valve 17, and associated auxiliary piping 19 and 19'. Inequipment of this type the inside coil 11 is located within the area tobe served by the heat pump, while the outside coil 13 is usually locatedin the ambient area.

During the normal cooling cycle the compressor 15 discharges arelatively hot gaseous refrigerant through the four-way reversing valve17 through a portion ofthe system including the auxiliary piping 19 inorder to obtain the desired cooling effects. The reversing valve 17 iscontrolled by electrical switching means 18. From the outside coil 13where condensation of the hot gaseous refrigerant occurs as ambient airis blown over the surface thereof by fan 21 driven by motor 23.

Liquid refrigerant formed in the coil flows through a suitable expansiondevice 24 to an indoor coil 11 serving as an evaporator. In this indoorcoil the liquid refrigerant is converted to a vaporous refrigerant as itextracts heat from a stream of air diverted over the coil by fan 25driven by motor 27. The vaporous refrigerant which is formed therebythen flows again through the reversing valve 17 into the compressor 15thereby completing the refrigerant cycle.

As has been brought out previously, when the temperature of the ambientair and the moisture contained therein are such that frost is formed onthe coil of an outside heat exchanger, in order to preserve theefficiency of the system, it is necessary to defrost the unit. Thisinvention functions as a defrost control for an air-to-air heat pump ofthe type hereinabove described and the control will operate and defrostthe outside coil only when defrosting is needed. This control willdefrost the coil under all normal operating conditions and will defrostcompletely before the control will terminate the defrost cycle. Inaddition, there is provided an auxiliary heating element 61 which may beplaced in service to maintain the duct heat during the defrost periodwhen the system is being used as a heater.

In accomplishing this function a'first capillary reference element 31 isinstalled in the outside air stream before the air enters the outsidecoil. A second capillary reference element 33 is located adjacent to theauxiliary piping 19 and interposed between the outside coil 13 and thefour-way reversing valve 17. Capillary reference bulb element 31 isconnected to bellows power element 35 while capillary reference bulb 33is connected to bellows power element 37. These reference capillary andpower elements are so chargedand located above the initiation leverassembly 39 to initiate defrost when the differential temperatureincreases to ten degrees to thirty degrees between the outside ambientair temperature which is represented by capillary reference element 31and the defrost initiation capillary reference element 33. Thisten-degree to thirty-degree differential will be less than if theevaporator is free of frost.

Adjustment of the temperature difference may be made by moving the powerelements 35 and 37 on the case 38 relative to the pivot point of thehinge pin initiation lever assembly 39.

In the event that frostor icing causes blockage of the air flow over theoutside coil, the coil temperature sensed by defrost initiationcapillary reference element 33 will lower rapidly and cause an increasein temperature differential between that point and the referencetemperature sensed by capillary reference element 31. This will causethe power element 35 to exert more pressure on the initiation leverassembly 39 than is caused by power element point is adjustable tovarying frost conditions. In addi-' 37. This difference in the forceresults in the initiation lever assembly rotating about its hinge pinand in so doing causes toggle switch 41 to change its position and cutoff outside motor 23 and thereby stopping fan 21. In addition theclosing of the electrical contacts in toggle switch 41 initiatesinterconnecting electrical switching means 18 whereby the four-wayreversing valve will change position and allow hot gas to enter theoutside coil. This hot gas will initiate coil defrosting. The coil willdefrostprogressively from inlet side 43.0f coil 13 to outlet 45 of coil13. Outlet side 45 being the last part of the outside coil 13 to defrostthereby assuring that a complete defrost will be accomplished each cyclebefore the unit can terminate defrost and reverse to a normal heatingcycle.

When outlet side 45 has reached a temperature of 4547 degrees, thedefrost capillary reference element 47 will actuate defrost power unit49 which will develop sufficient power due to its long arm throughtermination lever assembly 51 to overdrive initiation lever assembly 39and operate switch 41v which will then be positioned to cause thereversing valve to return to its normal cooling position and start motor23 and fan 21.

The auxiliary heat relay will be dropped out unless the structureheating thermostat 53 calls for auxiliary heat.

Initiation temperature adjustment means 55 is located proximate the endof initiation lever assembly 39-opposite the hinge pin. Initiationtemperature adjustment means 55 comprises a thumb screw adjustment whichis connected by biasing means to the end of said initiation leverassembly 39.

A similar termination temperature adjustment means 57 is located on thetermination lever assembly 51 proximate the end opposite its pivotpoint. Said adjustment means being adjustable between 40 and degrees.

From the foregoing it will be clear that applicant has provided a novelautomatic defrosting means wherein cut-off points or defrost initiationpoints operate only when they are needed and only when the outside coilis fully refrigerated .and/ or closed with frost. This cut-off tion thiscontrol allows the separate and independent adjustment of thetermination temperature of the defrost cycle. Further this defrosttermination occurs only when the outlet 45 is completely freeof frost orice and then and only then will termination lever assembly 51 beactuated to return the system to the structure heating cycle.

There is provided a case heater 59 and automatic thermostat means 53 forthe maintenance of an even operation ambient within and surrounding thepower elements. This will counteract the problems of the temperaturecontrol case being located in colder ambients and the termination powerelement bellows thereby causing a paralyzed condition of the powerelement bellows and rendering this side of the cycle non-operated.

It may be desirable in some applications to obtain the same result byenlarging the reference capillary elements so that liquid is alwayspresent in the bulb thereof, thereby preventing paralysis of thebellows.By so doing, the necessity for heating the case is obviated.

While only one embodiment of the invention has been shown by way ofillustration, there are many changes which may be obvious to one skilledin the art, and the scope of the invention is limited only by theappended claim.

I claim:

A control unit for controlling the defrost cycle of an ai-r-to-air heatpump comprising,

a case,

a first lever, pivotally mounted in said case,

first and second power elements adjustably mounted on said case fordifferential cooperation with said first lever,

a second lever pivotally mounted in said case,

a third power element adjustably mounted on said case for cooperationwith said second lever,

References Cited by the Examiner UNITED STATES PATENTS Lathrop 62210 XJones 62160 X Fifield 62160 X Felter 6216O Krueger 62-209 X thermostaticmeans for controlling said heating means. 10 LLOYD L. KING, PrimaryExaminer.

